Effect of Fluorene Groups on the Properties of Multiblock Poly(arylene ether sulfone)s-Based Anion-Exchange Membranes

Two kinds of novel multiblock poly(arylene ether sulfone)s were synthesized via block copolycondensation of telechelic oligomers as a starting material for the preparation of anion-exchange membranes (AEMs). The as-synthesized copolymers have extremely similar main chains. The difference is that the benzylmethyl groups for one are located on the fluorene-sulfone segments and they are located on the isopropylidene-sulfone segments for the other. The benzylmethyl moieties served as precursors to cationic sites and were brominated using N-bromosuccinimide (NBS) and then quaternized with N,N,N',N'-tetramethyl-1,6-diaminohexane (TMHDA). Controlled bromination and quaternization at specific positions of the benzylmethy-containing fluorene-sulfone segments and isopropylidene-sulfone segments can be achieved. 1H NMR spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography were used to characterize the as-synthesized copolymers. Distinct microphase separation in the as-prepared AEMs was observed using small-angle X-ray scattering and transmission electron microscopy. The AEM containing fluorene-sulfone segments (IEC=1.89 meq·g(-1)) showed higher ionic conductivity and methanol permeability than that containing isopropylidene-sulfone segments (IEC=2.03 meq·g(-1)). Moreover, the former showed better alkaline stability than the latter.